As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(AUS) AFTER FIVE MINUTES OF AEROBATICS A LOW OIL PRESSURE INDICATIONWAS NOTED. GROUND CHECK FOUND THE ENGINE OIL QUANTITY OK. ONREMOVAL OF THE AEROBATIC OIL SYSTEM VALVE ASSEMBLY BOTTOM PLUG A1/4IN UNC SCREW WITH ATTACHED LOCKWASHER WAS FOUND. SUSPECT SCREW WAS A LYCOMING ROCKER HAT SCREW. PERSONNEL/MAINTENANCE ERROR. FOD